Rotary heat exchanger



March 1958 F.-F..M|,sKELL 2,825,149

ROTARY HEATEXCHANGER Filed April 13, 1955 I @LAJFQW/QM I g; all,

staggered one from another.

United States Patent ROTARY HEAT EXCHANGER Ford F. Miskell, Milwaukee, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application April 13, 1955, Serial No. 501,020

1 Claim. (Cl. 34-436) The present invention relates generally to a rotatable device for treating a material with gas and more particularly to a rotatable heat exchanger comprising helical lifters for cascading, tumbling and conveying the material through the heat exchanger.

One prior art rotatable heat exchanger comprises a rotatable cylindrical shell. Upon the internal surface of the shell is mounted a plurality of straight lifters axially parallel to each other. At one end of the shell, means are provided for feeding material into the shell. At the other end of the shell, means are provided for discharging treated material from the shell. The feed end of the shell is elevated relative to the discharge end. A flow of hot gas passes through the rotating shell from one end to the other. When the shell is rotated the material within the shell is cascaded, tumbled and conveyed axially through the shell by the combined action of the lifters, the shell wall and gravity. The material as it passes through the shell exchanges heat with the gas flowing through the shell. In this way, a wet feed material can be dried.

A disadvantage of this prior art heat exchanger is that it has poor thermal efficiency since much of the hot gas passes through the entire length of the shell without contacting any of the feed material.

A second prior art heat exchanger comprises two discrete coaxially nested inclined cylinders defining a material treating annular space therebetween. On the inner surface of the cylinder of greatest radius are mounted a plurality of axially and radially extending lifters of Z shape. A similar number of axially and radially extending lifters of Z shape are mounted on the annulus-defining surface of the cylinder of least radius. The lifters are arranged so that the lifters on the opposed surfaces are The lifters are not axially continuous from one end of the heat exchanger to the other but rather are composed of pieces of comparatively short axial length. The lifters end at some little distance above the lower end of the cylinder so that the heated material which is fed into the heat exchangers annular space can slide freely to the bottom of the heat exchanger and out the discharge end. As the heat exchanger is rotated, the material is brought into contact with the annulus-defining surface of the inner cylinder. Cooling water is continuously circulating through this inner cylinder. The cooling water keeps the inner cylinder cool. The cooler inner cylinder therefore absorbs heat from the hotter material passing through the heat exchanger and cools the material. The cooled material is transported tothe discharge end by an effective force of gravity re sulting from the inclination of the cylinders.

A disadvantage of this prior art heat exchanger is that it provides only a relatively limited region in which heat transfer can occur in comparison to its external dimensions since a great deal of. its potential heat exchange region is used for the passage of the liquid coolant.

Another disadvantage, of this heat exchanger is that the rate of heat transfer obtainable from it is not as great as current industrial usage demands.

2,825,149 C6 Patented Mar. 4, 1958 A further disadvantage of this type of heat exchanger is that it does not permit the intimate contact of the cooler material with the hotter material desirable for efiEicient heat transfer.

A still further disadvantage of this type of heat exchanger is that it has a limited capacity and is therefore not readily adapted for many of the uses to which a heat exchanger may be needed.

A third prior art heat exchanger comprises two discrete coaxially nested inclined cylinders defining an annular space therebetween. A plurality of axially extending shelves extend across the annular space between the cylinders to define a plurality of axially extending compartments within the annular space. The shelves are tangential to the inner cylinder and are provided on both sides with a series of longitudinal ribs over which material to be dried is dribbled as the drier revolves. A plurality of radially extending separators are fastened to the annulus defining surface of the outer cylinder in each of the compartments. Each of these separators is likewise provided with a series of longitudinal ribs on both sides thereof. Hot gas is passed countercurrently to the direction of flow of the material through the annular space where it intimately contacts Wet feed material. The dribbling of the feed material during rotation of the drier exposes the material for drying by the gas. The material is conveyed to the discharge end by the combined action of the shelves, the cylinders and the eiiective gravitational force resulting from the inclination of the drier.

A disadvantage of this heat exchanger is that it provides only a relatively limited region in which heat transfer can occur in comparison to its external dimensions since much of its potential heat exchange region is used by the inner cylinder through which no material to be treated is passed.

A further disadvantage of this heat exchanger is that it must be inclined for the feed material to be effectively transported therethrough without auxiliary means of motivation.

The present invention proposes to overcome the aforementioned disadvantages of the prior art. The present invention also proposes to increase the heat exchange region of the heat exchanger relative to its external dimensions by providing an unobstructed opening in which heat exchange can occur. The present invention further proposes to present a greater quantity of feed material, than presented by the prior art devices, for intimate contact with flowing gas by means of rotatable heat exchanger comprising a plurality of axially extending helical lifters, having an angle of spiral less than the angle of repose of the feed material, which lifters produce a plurality of curtainlike treatment surfaces substantially throughout the heat exchanger when it is rotated.

Accordingly, it is the primary obect of the present invention'to provide an improved heat exchanger which overcomes the aforementioned disadvantages of the prior art devices.

A further object of the present invention is to provide a rotary heat exchanger having a greater rate of heat exchange, a larger heat exchange region, a greater capacity, and an improved thermal efficiency than prior art devices have for a given diameter.

. A further object of the persent invention is to provide a rotary heat exchanger comprising a plurality of helical lifters disposed therein having an angle of spiral less than the angle of repose of the material being treated.

A still further object of the present invention is to provide an improved heat exchanger in which the material to be treated can progress through the device when it is horizontally disposed.

Still further objects will be apparent and the invention will appear more clearly from the following detailed the 3 scription and the accompanying drawing showing several embodiments of this invention.

The same reference characters refer to like parts in the several figures.

in the drawing:

Fig. 1 is a side elevation showing a rotary heat exchanger embodying the present invention;

Fig. 2 is a section taken along line II-II of Fig. 3 of a rotary heat exchanger embodying the present invention in which all but one of the helical lifters has been removed for the sake of clarity;

Fig. 3 is an end view of the discharge end of the rotary heat exchanger shown in Fig. 2;

Fig. 4 is a section taken along line IVIV of Fig. 5 of a preferred embodiment of a rotary heat exchanger illustrating the present invention;

Fig. 5 is an end view of the discharge end of the rotary heat exchanger shown in Fig. 4;

Fig. 6 is an end elevation of the discharge end of an alternative embodiment of a heat exchanger similar to that shown in Fig. 4 but in which helical lifters of L shape section have been substituted for the lifters shown in Fig. 4;

Fig. 7 is an end elevation of the discharge end of the rotary heat exchanger of Fig. 5 showing the improved curtains of material provided by the present invention.

Referring to the drawing, and more particularly to Fig. 1, the invention is exemplified in a rotary heat exchanger comprising a shell 11 having coaxial internal and external surfaces 12, 13, respectively. Shell 11 is mounted for rotation about its longitudinal axis in any suitable manner such as external annular flanges 16, 16 supported by rollers 17, 17, which in turn are supported by pedestals 18, 13. Shell 11 may be of any suitable shape, such as cylindrical, as is shown in the drawing.

it will be noted that the material has been omitted from all figures except Fig. 7 for the sake of clarity.

Shell 11 is further provided with means for introducing material therein and means for withdrawing material therefrom. These means may be of any suitable character such as for example, the hopper 2t) and gravity drop 21 shown in Fig. 1.

Any suitable means for conveying the discharged material away from the rotary heat exchanger of this invention may be adopted such as conveyer belt 22.

Any suitable means for rotating shell 11 may be used such as, for example, a driving sheave 25 mounted upon the drive shaft 26 of a motor 27 and connected for the transmission of motion by a V-belt 28 to a driven sheave 29 which is rigidly secured to the external surface 13 of shell 11.

Any suitable means for introducing the gases into the heat exchanger for effecting a heat transfer or exchange may be used such as, for example, exhaust blower 30. The gas may be any suitable gas, may originate from any convenient source of supply, such as combustion chamber 31, and may be of any desired flow such as the parallel flow illustrated in Fig. 1.

As is shown in Figs. 2 and 4, the internal surface 12 of shell 11 is provided with a helical lifter 33 mounted thereon. The lifter may be of a Z shape, as shown in Fig. 3, or of an L shape, as shown in Fig. 6.

As shown in Fig. 7, each lifter of a Z shape maybe considered to comprise a first flange portion 35, a second flange .or rib portion 36, and an intermediate portion or flange 37 intimately interposed between first flange portion35 and second flange portion 36. Each lifter of an L shape comprises a rib portion 36' and aflange 37 as shown in Fig. 6.

Flange or intermediate portions 37, 37 and rib por- The dimensional relationship of the portions of the helical lifters to each other and to the shell 11 is illustrated in Fig. 6 Where: A is the dimension measured along radius of shell 11 of flange 37' of helical lifter 43' (various of the lifters of the heat exchanger of Fig. 6

used for sake of clarity of illustration); B is the distance which rib portion 36' extends in the direction of rotation of shell 11 (shown as clockwise for illustrative purposes only); R is the internal radius of curvature of s ell, 11; and W is the variable angle defined by the mabearing surface of the rib, portion 36 projected to intersect with the extended horizontal diameter of shell 21, measured at a section such as that shown in Fig. 6. The same relationships apply, of course, to the structure iilustrated by Fig. 7.

A preferably ranges from A R to /6 R, and B preferably ranges from /3 A to A or approximately from R to A R.

W, it will be observed, increases as the helical lifter advances in the direction of rotation of shell 11. When the angle W equals the angle of repose of the feed material, the bin 40 of the lifter will be evacuated.

As used herein, angle of spiral is that angle defined by a helical lifter and a longitudinal element of the shell which intersects the helical lifter. It is preferred that the angle of spiral for any given flight, for example, flight 33, be an angle which is greater than 0 but not greater than the angle of repose of the feed material.

As used herein, feed material is any material, preferably granular, which may be introduced into the heat exchanger of this invention for effecting a heat trans for with the gases flowing through the heat exchanger.

As herein used, angle of repose is that base angle to which a given material may be pyramided without lateral slippage, i. e., the natural angle formed by a given material when it is piled.

If the angle of spiral exceeds the angled repose, the improved material treating characteristics of this invention will not be achieved and the helical lifter will serve merely as a screw type conveyer. When the angle of spiral is less than the angle of repose of the material be ing treated but greater than zero, the material will both be showered and conveyed in a manner to be more fully described. The minimum angle of spiral in a preferred embodiment of the present invention is the angle formed when each lifter, in a shell containing N lifters, makes one 360 turn within the shell while traversing the length of the shell. In other words, the angle of spiral 0c is equal to 1rd arc tan where 1r is 3.14, d is the diameter of the shell and l is the distance measured on the longitudinal axis of the shell to advance one helical lifter one complete turn of 360. To put it another way, I is that length of shell in which a line drawn on the surface of the shell parallel to the axis thereof, i. e., a longitudinal element of the shell, will intersect a given helical lifter at two points. if the actual length of the shell is not at least equal to l, i. e.. the length of shell necessary for one lifter to complete one 360 turn in the shell at the given angle of spiral, then the maximum results of the present invention will not be realized. In other words, for optimum results the actual length of the shell shall be at least equal to l.

in Fig. 4, a preferred embodiment of the heat exchanger of the invention is shown having a plurality of similar helical lifters, 33, 41, 42, 43, 44- and 45.

Rib portion 36 of lifter 33, and the corresponding por' tions of the other similar lifters, 41-45 inclusive, define in part an uninterrupted open space 48 disposed therebetween.

In Fig. 6, an alternative embodiment of the heat exchanger of the invention is shown having a plurality of similar helical lifters of L shape 33, 41', 42', 43', 44' and 45'. The description of lifters 33, 41, 42, 43, 44 and 45 apply equally to lifters 33', 41, 42', 43', 44' and 45'.

During rotation, the angle W, as the segment of a lifter (as shown in Fig. 6), passes through its topmost position, gradually increases and causes a substantially continuous discharge of material from the lifter to provide a curtain of material shown in Fig. 7. The combined action of all the lifters provides a plurality of curtains 50. As each lifter proceeds upward, therefore, its carrying capacity is lessened and the material it was carrying gradually rolls 01f its inner edge.

The heat exchanger operates as follows: motor 27 and blower 30 are energized and the material to be treated is introduced into the rotating shell 11 through hopper 20. The material piles upon the bottom of shell 11 from where it is scooped into the reservoirs or bins 40 of the rotating helical lifters 33, 41-45 inclusive. The material is then raised by the rotating helical lifters 33, 4145 inclusive. As each lifter proceeds upward, its carrying capacity is lessened until angle W approaches the angle of repose of the material at which time the remainder of the material contained in the angle between flange 36 and rib 37 begins to leave the lifter. The gradual variation of angle W and the upward advance of the lifters provides a substantially continuous shower of material from the lifters through the unobstructed opening 48 defined by and extending between the ribs 36. The showering material from the succession of lifters produces a plurality of a curtainlike curved heat exchanging surfaces 50 throughout a major portion of the region enclosed in shell 11. The curtains 50 are substantially transverse the axis of the shell 11 and extend to a point at which the angle made by material bearing surface of rib 36 with the horizontal is equal to the angle of repose of the material.

The treating gases passing through the shell are intro duced to the curtains of material and heat exchange is thereby efiected.

When all of the material to be treated has passed through the shell 11, the device is turned olr" simply by deenergizing motor 27 and blower 30.

While only two embodiments have been illustrated and described herein, it is understood that they in no way limit the scope of this disclosure which is limited only by the appended claim.

It is claimed and desired to secure by Letters Patent:

A rotary heat exchanger having a cylindrical shell mounted horizontally for rotation about its longitudinal axis and provided with an inner surface, means for introducing material into and withdrawing material from the shell, and single means for passing gases through the shell in combination with means cooperating with the a shell for conveying and showering material therethrough comprising a plurality of continuous helical lifters mounted to the inner surface of the shell and defining with a longitudinal element thereof an angle which is greater than zero degrees but not more than the angle of repose of the material, each of said lifters further comprising a flange extending radially from the inner surface of the shell for a distance of from R/4 to 4/ 6, where R equals the internal radius of curvature of the shell, and a continuous rib mounted substantially normal to said flange and extending generally in the direction of rotation of the shell for a distance'of from about R/ 18 to a about R/4, where R is again equal to the internal radius of curvature of the shell.

4 References Cited in the file of this patent UNITED STATES PATENTS 1,297,409 Shatto Mar. 18, 1919 1,703,635 Ranson Feb. 26, 1929 2,264,646 Spears Dec. 2, 1941 V U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 25825 149 March 4, 1958 Ford F Miskell It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let ters Patent should read as corrected below.

Column 6, line 25, for "4/6" reed R/ Signed and sealed this 22nd day of April 19580 (SEAL) Attest: KARL Ho. K LINE ROBERT C. WATSON Attestin Officer Conmissioner of Patents 

